The goals are to define the structural and biochemical properties of domains of the spermatozoan plasma membrane which relate to their specific functions in the fertilization process; second, to define how these domains are modified during post-testicular development; and, third, to determine how these modifications contribute to the development of motility and fertilizing capacity. The specific objectives are 1) to determine the site of synthesis, localization on the sperm surface and the fate during fertilization of sperm-binding polypeptides secreted by the epididymis; 2) to characterize the binding of epididymal secretory polypeptides to the sperm plasma membrane; 3) to identify functional alterations in spermatozoa which result from the binding of epididymal luminal fluid polypeptides; 4) to determine if some epididymal secretions function as zona pellucida binding components; and 5) to define the processing and function of major polypeptide components of epididymal luminal fluid which appear transiently and do not bind the sperm surface. For these aims monospecific antibodies will be prepared against a set of epididymis-derived, sperm-associated polypeptides we have previously characterized. Immunohistochemical techniques will be employed to localize polypeptide distribution in the epididymal epithelium and over the sperm surface and to trace the fate of the polypeptides during fertilization in vivo. Both intact spermatozoa and plasma membranes isolated from spermatozoa by nitrogen cavitation will be examined for physiological and biochemical responses to purified epididymal polypeptides; in addition, we will identify epididymal polypeptides that might function as recognition or binding factors during sperm-egg interaction. Finally, we will examine the mechanism by which transient, major polypeptides, of the epididymal lumen are processed and test the possibility that they modify sperm function or affect the epididymal epithelium at sites distal to their appearance. A resolution of these specific aims will contribute to our understanding of membrane physiology, post-testicular sperm maturation and the fertilization process.